I have now moved the GPUs into colder water as well. I wanted to chill them slightly, so I used a 10' piece of garden hose from the pump to the 1st GPU and made that garden hose go through the chiller through the 2 holes already in the lid.
Now they are idling ~10-15 C cooler( low 30s) and the hoses are no longer hot.
I'm very pleased.....I think I may use a longer piece of garden hose and cool them a little more. I decided submerging the radiator would get them too cold and I'd have condensation.